1. Field of the Invention
The present invention is directed generally to wireless communication systems and, more specifically, to transmission power control for data signals and control signals.
2. Description of the Art
A communication system includes DownLink (DL), which supports signal transmissions from a base station (i.e., a “Node B”) to User Equipments (UEs), and UpLink (UL), which supports signal transmissions from UEs to the Node B. UEs, which are also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may include wireless devices, cellular phones, personal computer devices, etc. Node Bs are generally fixed stations and may also be referred to as Base Transceiver Systems (BTS), access points, or other similar terminology.
UL signals contain data information, which may include Uplink Control Information (UCI). The UCI includes at least ACKnowledgement (ACK) signals, Service Request (SR) signals, Channel Quality Indicator (CQI) signals, Precoding Matrix Indicator (PMI) signals, or Rank Indicator (RI) signals. UCI may be transmitted individually in the Physical Uplink Control CHannel (PUCCH) or, together with other non-UCI data, in a Physical Uplink Shared CHannel (PUSCH).
ACK signals used in association with Hybrid Automatic Repeat reQuests (HARQs), will be referred to as HARQ-ACK signals, and are transmitted in response to correct or incorrect reception of Transport Blocks (TBs) transmitted through a Physical Downlink Shared CHannel (PDSCH). SR signals inform the Node B that a UE has additional data for transmission. CQI signals inform the Node B of the channel conditions that a UE experiences for DL signal reception, enabling the Node B to perform channel-dependent PDSCH scheduling. PMI/RI signals inform the Node B how to combine signal transmissions to a UE through multiple Node B antennas in accordance with a Multiple-Input Multiple-Output (MIMO) principle.
PUSCH or PDSCH transmissions are either dynamically configured through a Scheduling Assignment (SA) transmitted in the Physical Downlink Control CHannel (PDCCH) or periodically configured with parameters set through higher layer signaling. For example, such configuration may be performed through Radio Resource Control (RRC) signaling from a Node B to each respective UE.
A PUSCH transmission structure is shown in FIG. 1. A Transmission Time Interval (TTI) includes one sub-frame 110, which includes two slots. Each slot 120 includes NsymbUL symbols. Each symbol 130 includes a Cyclic Prefix (CP) to mitigate interference due to channel propagation effects. The signal transmission in the first slot may be located at the same or different part of the operating BandWidth (BW) than the signal transmission in the second slot. One symbol in each slot is used to transmit Reference Signals (RS) 140, which provide a channel estimate to enable coherent demodulation of the received data and/or UCI. The transmission BW includes frequency resource units, which will be referred to as Physical Resource Blocks (PRBs). Each PRB includes NscRB sub-carriers, or Resource Elements (REs), and a UE is allocated MPUSCH PRBs 150 for a total of MscPUSCH=MPUSCH·NscRB REs for a PUSCH transmission BW of the UE. The last symbol of the sub-frame may be used to transmit Sounding RS (SRS) 160 from at least one UE. The SRS mainly serves to provide a CQI estimate for the UL channel, thereby enabling the Node B to perform channel-dependent PUSCH scheduling. The Node B configures the SRS transmission parameters for a UE through RRC signaling. The number of sub-frame symbols available for data transmission is NsymbPUSCH=2·(NsymbUL−1)−NSRS, where NSRS=1, if the last sub-frame symbol is used for SRS transmission and NSRS=0 otherwise.
FIG. 2 illustrates a PUSCH transmitter block diagram. Coded CQI bits and/or PMI bits 205 and coded data bits 210 are multiplexed at block 220. If HARQ-ACK bits are also multiplexed, data bits are punctured to accommodate HARQ-ACK bits at block 230. SR information, if any, is included as part of data information. A Discrete Fourier Transform (DFT) of the combined data bits and UCI bits is then obtained at block 240, MscPUSCH=MPUSCH·NscRB REs at block 250 corresponding to the assigned PUSCH transmission BW are selected at block 255 based on information from the SA or from higher layer signaling, Inverse Fast Fourier Transform (IFFT) is performed at block 260, and finally a CP and filtering are applied to the signal at blocks 270 and 280, respectively, before transmission at block 290. For clarity and conciseness, additional transmitter circuitry such as digital-to-analog converters, analog filters, amplifiers, and transmitter antennas are not illustrated. The encoding process for data bits and CQI and/or PMI bits, as well as the modulation process, are also omitted for clarity and conciseness. The PUSCH transmission may occur over clusters of contiguous REs, in accordance with the DFT Spread Orthogonal Frequency Multiple Access (DFT-S-OFDM) principle, which allows signal transmission over one cluster 295A (also known as Single-Carrier Frequency Division Multiple Access (SC-FDMA)), or over multiple clusters 295B.
At the receiver, reverse (complementary) transmitter operations are performed. FIG. 3 illustrates the reverse transmitter operations of the transmitter operations illustrated in FIG. 2. After an antenna receives the Radio-Frequency (RF) analog signal at 310, which may be processed by processing units such as filters, amplifiers, frequency down-converters, and analog-to-digital converters (not illustrated), a digital signal is filtered at block 320 and the CP is removed at block 330. Subsequently, the receiver unit applies a Fast Fourier Transform (FFT) at block 340, selects 345 the MscPUSCH=MPUSCH·NscRB REs 350 used by the transmitter, applies an Inverse DFT (IDFT) at block 360, extracts the HARQ-ACK bits and places respective erasures for the data bits at block 370, and de-multiplexes, at block 380, output of block 370 into data bits 390 and CQI/PMI bits 395. Regarding the transmitter, well known receiver functionalities such as channel estimation, demodulation, and decoding are not shown for clarity and conciseness.
A structure for the HARQ-ACK signal transmission in the PUCCH in one sub-frame slot is illustrated in FIG. 4. A transmission in the other slot, which may be at a different part of the operating BW, may have the same structure as the slot illustrated in FIG. 4, or alternatively, as with the PUSCH, the last symbol may be punctured to transmit SRS. The PUCCH transmission for each UCI signal is assumed to be within one PRB. The HARQ-ACK transmission structure 410 includes the transmission of HARQ-ACK signals and RS. The HARQ-ACK bits 420 are modulated, at block 430, according to a “Constant Amplitude Zero Auto-Correlation (CAZAC)” sequence 440, for example with Binary Phase Shift Keying (BPSK) or Quaternary Phase Shift Keying (QPSK) modulation, which is then transmitted after performing the IFFT operation. Each RS 450 is transmitted through the unmodulated CAZAC sequence.
A structure for the CQI/PMI transmission in the PUCCH in one sub-frame slot is illustrated in FIG. 5. The CQI transmission structure 510 includes the transmission of CQI signals and RS. The CQI bits 520 again are modulated, at block 530, according to a CAZAC sequence 540, for example using QPSK modulation, which is then transmitted after performing the IFFT operation. Each RS 550 is again transmitted through the unmodulated CAZAC sequence.
An example of CAZAC sequences is determined according to
            c      k        ⁡          (      n      )        =      exp    ⁡          [                                    j            ⁢                                                  ⁢            2            ⁢                                                  ⁢            π            ⁢                                                  ⁢            k                    L                ⁢                  (                      n            +                          n              ⁢                                                n                  +                  1                                2                                              )                    ]      where L is the length of the CAZAC sequence, n is the index of an element of the sequence n={0, 1, . . . , L−1}, and k is the index of the sequence. If L is a prime integer, there are L−1 distinct sequences which are defined as k ranges in {0, 1, . . . , L−1}. If a PRB includes an even number of REs, such as, for example, NscRB=12, CAZAC sequences with an even length can be directly generated through a computer search for sequences satisfying the CAZAC properties.
FIG. 6 shows a transmitter structure for a CAZAC sequence. The frequency-domain version of a computer generated CAZAC sequence 610 is described, as an example. The REs of the assigned PUCCH PRB are selected at block 620 for mapping, at block 630, the CAZAC sequence An IFFT is performed at block 640, and a Cyclic Shift (CS) is applied to the output at block 650. Finally, a CP and filtering are applied at blocks 660 and 670, respectively, before transmitting the signal at block 680. Zero padding is inserted by the reference UE in REs used for the signal transmission by other UEs and in guard REs (not shown). Moreover, for clarity and conciseness, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas as they are known in the art, are not shown.
Reverse (complementary) transmitter operations of the operations illustrated in FIG. 6 are performed for the reception of the CAZAC sequence, as illustrated in FIG. 7. Referring to FIG. 7, an antenna receives an RF analog signal at block 710. After processing by processing units such as filters, amplifiers, frequency down-converters, and analog-to-digital converters (not shown), the received digital is filtered at block 720 and the CP is removed at block 730. Subsequently, the CS is restored at block 740, a Fast Fourier Transform (FFT) is applied at block 750, and the transmitted REs are selected at block 765 based on information from the SA or from higher layer signaling. FIG. 7 also shows the subsequent correlation 770 with the replica 780 of the CAZAC sequence in order to obtain an estimate of the channel medium (possibly modulated by HARQ-ACK information or CQI information as shown in FIG. 4 or FIG. 5, respectively). Finally, the output 790 is obtained, which can then be passed to a channel estimation unit, such as a time-frequency interpolator, in case of a RS, or can to detect the transmitted information, in case the CAZAC sequence is modulated by HARQ-ACK information or CQI.
When UCI and data transmission occur in the same sub-frame, UCI may be transmitted together with data in the PUSCH or separately from data in the PUCCH. Including UCI in the PUSCH avoids simultaneous PUSCH and PUCCH transmissions, thereby conserving transmission power and avoiding an increase in the Peak-to-Average Power Ratio (PAPR) or the Cubic Metric (CM) of the combined signal transmission. Conversely, separately transmitting UCI in the PUCCH preserves PUSCH REs for data transmission and utilizes pre-allocated PUCCH resources. The required transmission power can be one of the conditions used to decide whether to simultaneously transmit PUCCH and PUSCH, to transmit UCI with data in the PUSCH, or to even transmit only UCI in the PUCCH and suspend the PUSCH transmission.
Transmission Power Control (TPC) adjusts the PUSCH or PUCCH transmission power to achieve a desired target for the received Signal to Interference and Noise Ratio (SINR) at the Node B, while reducing the interference to neighboring cells and controlling the rise of Interference over Thermal (IoT) noise, thereby ensuring the respective reception reliability targets. Open-Loop (OL) TPC with cell-specific and UE-specific parameters is considered with the capability for the Node B to also provide Closed Loop (CL) corrections through TPC commands. The TPC commands are included either in the SA configuring a dynamic PDSCH reception (TPC command adjusts the subsequent HARQ-ACK signal transmission power) or PUSCH transmission (TPC command adjusts the PUSCH transmission power), or are provided through a channel in the PDCCH carrying TPC commands (TPC channel) for PUSCH or PUCCH transmissions configured to occur periodically.
A TPC operation is described as follows based on the TPC operation used in 3rd Generation Partnership Project (3GPP) Evolved-Universal Terrestrial Radio Access (E-UTRA) Long Term Evolution (LTE). The PUSCH transmission power PPUSCH from a UE in reference sub-frame i is set according to Equation (1):PPUSCH(i)=min{PMAX,10·log10 MPUSCH(i)+P0—PUSCH+αPL+ΔTF(i)+f(i)} [dBm]  (1)where                PMAX is the maximum allowed power configured by RRC and can depend on the UE power amplifier class.        MPUSCH (i) is the number of (contiguous) PRBs for PUSCH transmission.        P0—PUSCH controls the mean received SINR at the Node B and is the sum of a cell-specific component PO—NOMINAL—PUSCH and a UE-specific component PO—UE—PUSCH provided by RRC.        PL is the DL path-loss estimate from the serving Node B as calculated in the UE.        α is a cell-specific parameter provided by RRC with 0≦α≦1. Fractional TPC is obtained for α<1 as the path-loss is not fully compensated. For α=0, pure CL TPC is provided.        ΔTF(i)=10·log10(2Ks·TBS(i)/NRE(i)−1) where Ks≧0 is a UE-specific parameter provided by RRC, TBS(i) is the TB size, and NRE(i)=MPUSCH (i)·NscRB·NsymbPUSCH(i) Therefore, TBS(i)/NRE(i) defines the number of coded information bits per RE (Spectral Efficiency (SE)). If Ks>1, such as Ks=1.25, ΔTF(i) enables TPC based on the SE of the PUSCH transmission. TPC based on the SE of the PUSCH transmission is useful when the adaptation of the PUSCH Modulation and Coding Scheme (MCS) is slow and tracks only the path-loss. With MCS adaptation per PUSCH transmission, PUSCH power variations depending on SE should be avoided and this is achieved by setting Ks=0.        f(i)=f(i−1)+δPUSCH(i) is the function accumulating the CL TPC command δPUSCH(i) included in the SA configuring the PUSCH transmission in sub-frame i, or in a TPC channel in the PDCCH, with f(0) being the first value after reset of accumulation.        
The PUCCH transmission power PPUCCH from a UE in reference sub-frame i is set according to Equation (2):PPUCCH(i)=min {PMAX,P0—PUCCHPL+h(•)+ΔF—PUCCH+g(i)} [dBm]  (2)where                P0—PUCCH controls the mean received SINR at the Node B and is the sum of a cell-specific component PO—NOMINAL—PUCCH and a UE-specific component PO—UE—PUCCH provided by RRC.        h(•) is a function with values depending on whether HARQ-ACK, SR, or CQI is transmitted.        ΔF—PUCCH is provided by RRC and its value depends on the transmitted UCI type.        g(i)=g(i=1)+δPUCCH (i) is the function accumulating the CL TPC command δPUCCH(i) in the PDCCH TPC channel or in the SA configuring the PDSCH reception and g(0) is the value after reset of accumulation.        
For the SRS, in order to avoid large power variations within sub-frame symbols when the UE transmits PUSCH and SRS in the same sub-frame i, the transmission power PSRS follows the PUSCH transmission power and is set according to Equation (3):PSRS(i)=min {PMAX,PSRS—OFFSET+10·log10MSRS+PO—PUSCH+α·PL+f(i)} [dBm]  (3)where                PSRS—OFFSET is a UE-specific parameter semi-statically configured by RRC        MSRS is the SRS transmission BW expressed in number of PRBs.        
In order to support data rates higher than data rates possible in legacy communication systems and further improve the spectral efficiency, BWs larger than BWs of a Component Carrier (CC) for legacy systems are needed. These larger BWs can be achieved through the aggregation of multiple legacy CCs. For example, a BW of 60 MHz is achieved by aggregating three 20 MHz CCs. A UE may perform multiple PUSCH transmissions during the same sub-frame in the respective UL CCs. FIG. 8 illustrates aggregation of multiple legacy CCs, where a UE has three PUSCH transmissions, PUSCH 1 810, PUSCH 2 820 and PUSCH 3 830, in parts of the BW of three respective UL CCs, UC CC1 840, UC CC2 850, and UL CC3 860, during the same sub-frame.
The TPC operation should therefore be extended to PUSCH transmissions from a UE in multiple UL CCs during the same sub-frame. Additionally, as PUSCH and PUCCH transmissions from a UE in the same sub-frame and in the same or different UL CCs are also supported, the TPC operation should also include the combined operation for the PUSCH TPC and the PUCCH TPC. As a UE may also have multiple PUCCH transmissions in the same sub-frame and in the same or different UL CCs, the PUCCH TPC operation should also include support for multiple PUCCH transmissions. As a UE may have multiple transmitter antennas, the TPC operation should support the signal transmission from multiple antennas.
Therefore, there is a need to define the PUSCH TPC operation for multiple PUSCH transmissions from a UE in the same sub-frame in the same UL CC and in multiple UL CCs. There is also a need to define the PUCCH TPC operation for multiple PUCCH transmissions, of the same or different UCI signals, from a UE in the same sub-frame in the same UL CC and in multiple UL CCs. There is also a need to define the TPC operation for multiple UE transmitter antennas. There is also a need to define the combined PUSCH and PUCCH TPC operation for multiple PUSCH transmissions and PUCCH transmissions from a UE in the same sub-frame in the same UL CC and in multiple UL CCs.